This is the schematic of the 1MB Memory Upgrade I developed. I'm still having trouble getting some small bugs out, so it's still in BETA-state. I hope you folks out there are willing to have a look at the upgrade. If you find bugs or if you tested it on your computer and everything works out 100% OK, please tell me so. Please contact me via mail or Email. Both addresses can be found at the end of this text. If you do contact me, please inform me about the computer you have and if you tested it with a device like the BlackBox, MIO, MCS-IDE interface, KPI/Supra Harddisk interface, PC-Bridge, etc. What is the purpose of this upgrade? To provide a memory upgrade for the XL/XE(GS) Atari computer that can be used on all XL/XE(GS) Atari computers and is as compatible to the 130XE as possible. Memory upgrades have been available for a long time. But most lost the separate access of ANTIC or CPU to the extended memory and quite a lot of them lost (software control over) BASIC, OSROM and the selftest. Some switch BASIC, OSROM and the selftest in and out when banks are switched. There were few upgrades for the XEGS. The once I know are either discontinued (Innovative Concepts) and to small or don't work because of errors in the refresh handling. My upgrade doesn't lose separate ANTIC and CPU access, (software control over) BASIC, OSROM, selftest or Missile Command but freezes the ROM enable lines going to the MMU when the RAMdisk is accessed. ROM's aren't switched around when banks are switched. My upgrade also doesn't use any weird addresses. Larger RAMchips only need to be told when to refresh. I used this in my upgrade. So the refresh problems that other upgrades have, because they rely on ANTIC to provide refreshcycles it never was intended to deliver, never happen with this memory upgrade. What's the current status? It works great on the XEGS, but it has no parallelbus. This means two things: - I can't test the parallelbus - Nowhere to plug my BlackBox in, so no hard disk access On my 800XL, it works OK. Untill I plug in the BlackBox. During boot up, the RED LED on the BlackBox normally lights up a few times. During the second period that this LED is on, the computer locks up. Sometimes sooner, sometimes later, but always while the LED is on for the second time. According to Bob Puff, SIO is accessed during this period. I tried the Stabilizer XL mod by Bob Puff but must have done something wrong. Now I get the selftest when I switch my 800XL on. With a lot of garbage. I hope to find out soon what went wrong here. I did get the tip that I should replace the 74LS138 with a 74F138. I'll try that one after I fix the Stabilizer thing. On my 800XE (in Germany the 800XL was the most popular Atari, so they called the 65XE 800XE. This 65XE (not the one sold in the USA and Canada) actually was a 130XE with only halve the memory, and no gate array (CO25953)), I keep having timing errors. With or without BlackBox. Funny thing is the 800XE/65XE is based on the XEGS. They both don't buffer the Phase zero clock, but buffer the GTIA select line. But my XEGS works fine. Maybe reversing this would fix the problem. Some (if not most) of these 800XE/65XE's had a buggy GTIA (made in China). I replaced the GTIA for one without bugs. That got rid of the Graphics 9 bug, but did nothing for the timing. The hardware: For now, a 1MB 30 pin SIMM is the maximum. 256kB SIMMs should work two. I hope to find an address range in the $D3xx range that isn't used by other upgrades, where we could stach an extra PIA, so 4MB or even 16MB would be possible. Why 16Mb? Cause it's fun! We need a CO25953 for the separate ANTIC and CPU access. If the computer doesn't have one, get one from Best Electronics or B&C Computervision. Maybe we need to replace the LS04 with an LS14. I tried it without an invertor. Doesn't work. You might ask yourself, what's he doing with the LS157? Well, without it, the signals going to the MMU are frozen way to long. This could get us into all kinds of trouble. You'll have to desolder the MMU. Pins 6, 9 and 18 are lifted. If you have an XEGS, pin 13 is also lifted. Be very carefull with this MMU, you can't get them in a hardware store. The XEGS uses a different MMU from the one in the XL and XE. The 1200XL and 1450XL use yet another MMU. Solder a precision IC socket where the MMU was. Push the pins of the MMU we didn't bend up into the socket. Be carefull that the MMU will be oriented the same way as before. I'm not sure if this upgrade will work on the 1200XL and 1450XL. According to Mapping the Atari (XL/XE edition), bits 2 and 3 of the 1200XL are used to indicate whether the keyboard is disabled and the international character set is switched on. As long as those are not changed during RAMdisk access, everything might work. But I'm not sure. If your computer has a FREDDY chip, but the motherboard has no provisions for 128kB of RAM, desolder pins 23 and 24 of FREDDY and bend them up carefully. This is where FA14 and FA15 are connected. If your computer has a FREDDY chip and the motherboard has provisions for 128kB of RAM, remove the zero Ohm resistors where it says U34 and put a precision socket inthere. Atari reserved 4 extra holes on the right, so you can use a 16 pin socket instead of a 20 pin socket. Leave the 4 right most holes filled with solder. If your computer doesn't have a FREDDY chip but two 74LS158 or 74LS258, desolder the pins contacted to A14 and A15 on one of these chips. Connect FA14 and FA15 where A14 and A15 were respectively. If you have an XL (600XL's need to be upgraded to 64kB first) or an XEGS desolder the resistor in the CAS line. You now have two holes where the resistor was. Connect the side not connected to the RAM chips to the CO25953. The other hole is connected to CASMAIN. If you have a computer with a 130XE motherboard, but only 64kB, you can find the CASBANK signal where the extra RAMchips would have been if Atari had decided to turn these computers into real 130XE's. If you have a 130XE, desolder the resistor in the CASBANK line on the side going to the RAM chips. The free end of the resistor is CASBANK. The only chips you will have to add to you computer are the chips starting with LS in my schematics. If you computer is not a 130XE (with 128kB), you will also have to add the CO25953. On the SIMM we do not need pins 26, 28 and 29. They are reserved for parity, which is needed in the PC world. Here's the pin out of a 30 pin SIMM: 1 +5V 16 DQ4 2 CAS 17 A8 3 DQ0 18 A9 4 A0 19 A10 5 A1 20 DQ5 6 DQ1 21 /WE 7 A2 22 GND 8 A3 23 DQ6 9 GND 24 A11 10 DQ2 25 DQ7 11 A4 26 PQ 12 A5 27 /RAS 13 DQ3 28 /PCAS 14 A6 29 PD 15 A7 30 +5V (Printed in 2 columns to save space. 4 columns gets a bit hard on a 40 columns screen. The SIMM ofcourse only has one row of pins.) I hope to have given you enough information so that you can build the upgrade into your computer. Since this is only a beta version (for now) and I'm placing this on the net so that people can help me to get it working on all the computers I mentioned (except MAYBE the 1200XL and 1450XL), I'm leaving out the information most people familiar wih (memory) upgrading our classic Atari already know or that is available on the net. As soon as the bugs are out, a small production run of printed circuit boards is planned. Thanks for helping me. CU Mathy van Nisselroy firstname@fullnamewithoutspaces.nl